This patent describes color manipulation for digital image processing in the prepress industry.
As a result of attempts to introduce more intuitive color manipulation, HSL (Hue, Saturation, Luminance) changes are executed in three steps. In the first step, the original image is translated from the printable CMY color space to the HSL (or equivalent) color space, which is unprintable, but which is convenient for manipulation. In the second step, the HSL changes are applied according to a binary mask and are executed in the new color space. In the third step, the new image is translated back to the printable color space. The original black remains unchanged in such color manipulation. EQU (CMY).sub.original .fwdarw.color space translation.fwdarw.[HSL(or equivalent)].sub.original EQU [HSL(or equivalent)].sub.original .fwdarw.HSLchange.fwdarw.[HSL(or equivalent)].sub.new EQU [HSL(or equivalent)].sub.new .fwdarw.color space translation.fwdarw.(CMY).sub.new
In this approach it is difficult to: 1) accomplish quality translations between color spaces; 2) meet precision requirements; 3) decide how to treat unprintable colors; 4) achieve interactive performance; 5) avoid the undesirable effects of binary weighting; and 6) not distort the original gray balance.